This invention relates to the mechanical softening of material that is in sheet form, such as paper sheets and the methods of manufacturing them. More particularly, this invention relates to tissue and towels that have increased softness.
The type and amount of fibers that extend out of a sheet have been known to effect the perceived softness of that sheet. Although, tissue sheets are principally discussed herein, it should be recognized that this invention is not limited to tissue sheets or products, but may be applicable to any type of paper product, as well as other types of material, such as non-woven and woven fabrics, where softness or the amount of loose fibers on the surface of the product is desirable. All other factors remaining equal, a tissue sheet that has more loose fibers on its surface, i.e., one that is fuzzier, should be perceived as being softer than a tissue sheet that has less loose fibers on its surface. By loose fibers as used herein, it is meant that one end of the fiber is not bonded to other fibers in the tissue sheet and is protruded above the bonded surface of the sheet. The desirability of increasing the number of loose fibers on the surface of a sheet to increase perceived softness has been know. For example, Wand U.S. Pat. No. 3,592,732, discloses using a brush to lift the fibers from the surface of a tissue or towel sheet to increase softness.
This invention is an improvement over the prior art in the type, and technique, of mechanical softening and in the product that is obtained. The apparatus and techniques of the present invention provide an improvement in production speed and efficiency. In one embodiment, a new tissue product is further provided that has selectively raised fibers over only a portion of the sheet surface. Such tissue product can be obtained by using the abrading apparatus and techniques on an uncreped through air dried tissue, such as those disclosed in U.S. Pat. No. 5,607,551, and copending U.S. patent application Ser. No. 08/310,186 filed Sep. 21, 1994, the disclosures of which are incorporated herein by reference.
In one embodiment of the invention there is provided a soft tissue product having increased surface fuzziness formed by abrading a tissue product comprising one or more tissue plies and having a MD Max Slope of about 10 or less.
In an alternative embodiment of the invention there is provided a soft tissue product having increased surface fuzziness formed by abrading an uncreped through dried web comprising at least about 10 dry weight percent high yield pulp fibers and wet:dry geometric mean tensile ration of about 0.1 or greater.
In an alternative embodiment of the invention there is provided a soft tissue sheet comprising: a first surface and a second surface; each surface comprising paper making fibers; and, at least one of the surfaces having selectively loosened areas of paper making fibers.
In an alternative embodiment of the invention there is provided a soft paper product comprising: a first layer and a second layer, the layers each comprising paper making fibers; a first and a second surface, the first surface corresponding to the surface of the first layer and the second surface corresponding to the surface of the second layer; and, at least one of the surfaces having loosened fibers thereon.
In an alternative embodiment of the invention there is provided a soft sheet product having a machine direction tensile strength of at least about 1000 grams per 3 inches and a cross-machine direction tensile strength of at least about 800 grams per 3 inches and comprising: a first surface and a second surface, each surface comprising fibers; and, at least one of the surfaces having substantial loosened fibers thereon.
In an alternative embodiment of the invention there is provided a paper sheet having an improved rate of absorbency comprising: a first sheet surface and a second sheet surface; a layer comprising paper making fibers; the layer having a surface; the surface of the layer corresponding to a surface of the paper sheet; the surface of the layer having abraded fibers; and the rate of absorbency of the sheet being greater than a sheet of similar composition but not having abraded fibers on its surface and the amount of absorbency for the sheet being comparable to the similar non-abraded sheet.
In an alternative embodiment of the invention there is provided a soft paper product comprising a layer; the layer comprising long papermaking fibers; the layer having a surface; the surface having a PR/EL of greater than about 0.72, or greater than about 1, and in which the surface layer has at least about 20% of the fields of view having a PR/EL ratio of about 2 or greater.
In yet a further embodiment of the present invention there is provided a method of making a sheet product having improved softness comprising: obtaining a web of fibrous material in sheet form feeding the web into an abrasion apparatus comprising: a pressure device; a backing roll; an abrasion roll; and abrading the surface of the web with the abrasion roll.
In an alternative embodiment of the invention there is provided a method of treating a paper web comprising: feeding a web of paper comprising papermaking fibers into a nip formed by a first and a second roller; the nip applying pressure to the web to hold the web against the second roller; the web partially wrapping and moving around and with the second roller; a third roller contacting the web while the web is against the second roller and the third roller having a rough surface; and, the third roller rotating while in contact with the web to loosen the fibers on the surface of the web.
In an alternative embodiment of the invention there is provided a method of treating a paper web comprising: obtaining a web of paper comprising papermaking fibers; bringing the paperweb in contact with a first roller; holding the web against the first roller; the web partially wrapping and moving around and with the first roller; a second roller contacting the web while the web is in contact against the first roller, the second roller having a rough surface; and, the second roller rotating while in contact with the web to loosen the fibers on the surface of the web.
In yet a further embodiment of the present invention there is provided an apparatus to treat webs of fibrous material comprising: a first roller; a second roller; a tensioning device; a frame to hold the rollers and device in a set relationship; the tensioning device positioned adjacent the first roller; the second roller positioned near the first roller, and set a distance of from about 0.006 inches to about 0.008 inches from the first roller; and, the second roller having an abrading surface of sufficient roughness to loosen fibers, only on the surface of the web being treated.
Mechanical softening by abrading the surface of a tissue sheet improves the feel of the sheet as perceived by the consumer or end user. Abrading works the surface of the sheet causing partial debonding of surface fibers giving rise to loose fiber ends on that surface, but without reducing the central strength of the sheet. Some potential advantages that may be obtained by abrading a tissue sheet include:
1) improved customer product perception in hand and in use for a given sheet;
2) reduced chemical costs by reducing the amount of chemical debonders required in the tissue and particularly in the outside layer of a multilayered tissue;
3) reduced fibers costs, including a reduction in the use of higher cost fiber processing, such as curling fibers;
4) improved strength for a given perceived softness;
5) reduced sidedness in a one-ply tissue or other one-ply webs;
6) reduced calender loading pressures, which would allow for less bulk reduction of the tissue during manufacturing; and,
7) improved rate of absorbency.